1. Field of the Invention.
The present invention pertains to electrical motors and more particularly, relates to solving the problem of end play variation occurring in a variety of motors when the tolerances involved for individual parts accumulate such that there is great difficulty in insuring that the end or axial play of the rotor will be kept to a minimum.
Although a certain degree of end play is normally permissible in the fabrication of a variety of electrical motors, one wants to insure that such axial movement will be minimized. Specifically, the present invention is particularly concerned with the problem of end play variation as it occurs in certain small so-called skeleton motors typically used for driving fans or brushes or the like.
Essentially, the above-described end play problem arises because of the fact that the distance between the front and rear bearings on such skeleton motors is determined mostly by the stack heights of the stator. The stator, in turn, can vary in its length by as much as plus or minus 0.040 inches in typical cases. When the accumulated tolerance of the various brackets used for mounting the bearings is taken into account, the distance between bearings can vary on some motors by as much as plus or minus 0.060 inches. Now, since the armature is mounted between these bearings, unless some arrangements are provided to adjust or compensate for this tolerance, the brushes could run over the commutator or into the welded connections thereof. In addition, the armature laminations would move out of alignment with stator laminations.
2. Background Art
In order to provide some background information for the disclosure of the present invention, reference may be made to U.S. Pat. No. 4,170,058 in which a particular method of adjusting end play is described. However, the method of that patent involves relative axial positioning between a bearing and one of the rotor and stator.
In contrast, the present invention provides an arrangement which does not involve displacement of a bearing. Instead, a totally different means is adopted to solve the problem of overcoming accumulated tolerance.
Accordingly, it is a primary object of the present invention to provide for adjustment of end play so as to compensate selectively for the variations that occur from one motor to another in the distance between their front and rear bearings, due to the variable accumulated tolerance which defines or determines the distance.
Another object is to provide an extremely simple means disposed around the shaft of the rotor for accomplishing the above-stated purposes.
Another object is to provide a method which ensures that the means which grips the shaft is properly positioned; i.e., is close to being abutted with the rotor bearing at the rear of the motor.